Calculate whether an IP address is in a specified range in Java

Question

I want to be able to return true/false depending on an IP being in range of two other IPs.

For instance:

ip 192.200.3.0

range from 192.200.0.0

range to 192.255.0.0

should result to true.

Other examples:

assert 192.200.1.0 == true
assert 192.199.1.1 == false
assert 197.200.1.0 == false

Answer 1

The easiest way to check the range is probably to convert the IP addresses to 32-bit integers and then just compare the integers.

public class Example {
    public static long ipToLong(InetAddress ip) {
        byte[] octets = ip.getAddress();
        long result = 0;
        for (byte octet : octets) {
            result <<= 8;
            result |= octet & 0xff;
        }
        return result;
    }

    public static void main(String[] args) throws UnknownHostException {
        long ipLo = ipToLong(InetAddress.getByName("192.200.0.0"));
        long ipHi = ipToLong(InetAddress.getByName("192.255.0.0"));
        long ipToTest = ipToLong(InetAddress.getByName("192.200.3.0"));

        System.out.println(ipToTest >= ipLo && ipToTest <= ipHi);
    }
}

Rather than InetAddress.getByName(), you may want to look at the Guava library which has an InetAddresses helper class that avoids the possibility of DNS lookups.